Piston pump for brake system

ABSTRACT

According to at least one aspect, the present disclosure provides a piston pump comprising: a piston unit configured to reciprocate by driving of a motor cam; a sleeve unit disposed to surround at least a part of the piston unit and having a space in which brake oil is stored; and a check valve unit facing the sleeve unit and discharging the brake oil to an outside of the sleeve unit when a pressure of the brake oil increases, wherein the piston unit includes a first piston having a first end in contact with the motor cam and reciprocating, a second piston having a first end coupled to a second end of the first piston and configured to press the brake oil, and a spring cap coupled to a second end of the second piston and disposed to accommodate an inlet spring therein.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority to Korean PatentApplication No. 10-2020-0116043, filed on Sep. 10, 2020 in the KoreanIntellectual Property Office, the entire disclosure of which isincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a piston pump for a brake system.

BACKGROUND

The information disclosed in the Background section herein is to aid inthe understanding of the background of the present disclosure, andshould not be taken as acknowledgement that this information forms anypart of prior art.

FIG. 1 is a schematic cross-sectional view illustrating a conventionalpiston pump for a brake system.

Referring to FIG. 1, a conventional piston pump 1′ includes a motor cam10 configured to perform cam movement by driving of a motor (not shown)and a piston unit 20 configured to linearly reciprocate in a pistonhousing 12.

The conventional piston unit 20 includes a piston body 22, a capcoupling portion 24 of which at least a part is coupled to a spring cap30, a step unit 26 having an outer diameter greater than an outerdiameter of the cap coupling portion 24 and having a function of astopper which restricts movement of the spring cap 30, and a pistonflange 28.

As the piston unit 20 reciprocates, the piston body 22 rubs against alow pressure sealing 40. In this case, a friction coefficient of anouter circumferential surface of the piston body 22 may be lowered forsmooth reciprocating movement of the piston unit 20. To this end, whenthe piston unit 20 is manufactured, a manufacturing process includes apolishing process.

Meanwhile, since the piston unit 20 has a complex shape in which the capcoupling portion 24, the step unit 26, and the piston flange 28 areconnected, the complexity and difficulty of the polishing process areincreased. Accordingly, there is a problem of increasing a defect ratewhen the piston unit 20 is manufactured.

In addition, although a portion, which rubs against the low pressuresealing 40, is limited when the piston unit 20 reciprocates, a polishingprocess is performed the entire piston body 22. Accordingly, due to anunnecessary polishing process, there is a problem of decreasingmanufacturing efficiency when the piston pump 1′ is manufactured.

In addition, since the piston unit 20 includes the step unit 26 and thepiston flange 28, the shape of the piston unit 20 is complex, and thusthere is a problem of increasing manufacturing costs.

SUMMARY

The present disclosure is mainly directed to a piston pump that canprovide a low defect rate and reduced manufacturing costs by removing anunnecessary polishing process.

In addition, the present disclosure is also directed to a piston pumpthat provides a high manufacturing efficiency.

The objectives to be solved by the present disclosure are not limited tothe objectives described above, and other objectives, which are notdescribed above, will be clearly understood by those skilled in the artthrough the following description.

According to at least one aspect, the present disclosure provides apiston pump comprising: a piston unit configured to reciprocate in apiston housing by driving of a motor cam; a sleeve unit disposed tosurround at least a part of the piston unit and having an accommodationspace in which brake oil is stored; and a check valve unit disposed toface the sleeve unit and configured to discharge the brake oil to anoutside of the sleeve unit when a pressure of the brake oil stored inthe accommodation space of the sleeve unit increases. The piston unitincludes a first piston having a first end in contact with the motor camand configured to reciprocate, a second piston having a first endcoupled to a second end of the first piston and operating in conjunctionwith reciprocating movement of the first piston to press the brake oilstored in the accommodation space of the sleeve unit, and a spring capcoupled to the a second end of the second piston and disposed toaccommodate an inlet spring therein.

According to another aspect, the present disclosure provides a pistonpump comprising: a piston unit configured to reciprocate in a pistonhousing by driving of a motor cam; a sleeve unit disposed to surround atleast a part of the piston unit, and having an accommodation space inwhich brake oil is stored; and a check valve unit disposed to face thesleeve unit and configured to discharge the brake oil to an outside ofthe sleeve unit when a pressure of the brake oil stored theaccommodation space of the sleeve unit increases. The piston unitincludes a first piston having a first end in contact with the motor camand configured to reciprocate, a second piston having a first endpress-fitted and coupled to a second end of the first piston andoperating in conjunction with reciprocating movement of the first pistonto press the brake oil stored in the accommodation space of the sleeveunit, and a spring cap disposed to accommodate an inlet spring thereinand coupled to a second end of the second piston.

According to the present embodiment described above, since a piston unitaccording to the present disclosure is formed as an assembly-typepiston, a polishing process is simplified, and thus there is an effectof lowering a defect rate. In addition, since the piston unit is formedin a simple structure, there is an effect of lowering manufacturingcosts.

In addition, since an unnecessary polishing process is removed, and thepiston unit having the simple structure is adopted, there is an effectof lowering manufacturing costs.

REFERENCE NUMERALS 1′: conventional piston pump 1, 6, 7: piston pump 10:motor cam 12: piston housing 14: inlet line 16: outlet line 20: pistonunit 30: spring cap 40: low pressure sealing 100, 600: piston unit 110,610: first piston 120, 620: second piston 130, 630: spring cap 140:inlet spring 150: inlet ball 160: first sealing 200: sleeve unit 300:check valve unit 400: filter

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentdisclosure will become more apparent to those of ordinary skill in theart by describing exemplary embodiments thereof in detail with referenceto the accompanying drawings, in which:

FIG. 1 is a schematic cross-sectional view illustrating a structure of aconventional piston pump for a brake system;

FIG. 2 is a schematic cross-sectional view illustrating a structure of apiston pump for a brake system according to one exemplary embodiment ofthe present disclosure;

FIG. 3 is an exploded cross-sectional view illustrating a piston unitaccording to one exemplary embodiment of the present disclosure isdissembled;

FIG. 4 is a cross-sectional view illustrating a state in which brake oilis supplied to an accommodation space of a sleeve unit according to oneexemplary embodiment of the present disclosure;

FIG. 5 is a cross-sectional view illustrating a state in which the brakeoil stored in the accommodation space of the sleeve unit according toone exemplary embodiment of the present disclosure is discharged to theoutside of the sleeve unit;

FIG. 6 is a schematic cross-sectional view illustrating a structure of apiston pump for a brake system according to another exemplary embodimentof the present disclosure;

FIGS. 7(A) and 7(B) show perspective views illustrating a piston unitaccording to another exemplary embodiment of the present disclosure; and

FIGS. 8(A) and 8(B) show cross-sectional views illustrating the pistonunit according to another exemplary embodiment of the presentdisclosure.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, some exemplary embodiments of the present disclosure willbe described in detail with reference to the accompanying drawings. Inthe following description, like reference numerals preferably designatelike elements, although the elements are shown in different drawings.Further, in the following description of some embodiments, a detaileddescription of known functions and configurations incorporated thereinwill be omitted for the purpose of clarity and for brevity.

Additionally, various terms such as first, second, A, B, (a), (b), etc.,are used solely to differentiate one component from the other but not toimply or suggest the substances, order, or sequence of the components.Throughout this specification, when a part ‘includes’ or ‘comprises’ acomponent, the part is meant to further include other components, not toexclude thereof unless specifically stated to the contrary. The termssuch as ‘unit’, ‘module’, and the like refer to one or more units forprocessing at least one function or operation, which may be implementedby hardware, software, or a combination thereof.

In addition, it should be noted that sizes, shapes, and movementdistances of elements of each of piston pumps 1 and 6 illustrated inFIGS. 2 to 8 may be expressed to be somewhat exaggerated and distortedfor clarity and convenience of description.

FIG. 2 is a schematic cross-sectional view illustrating a structure ofthe piston pump for a brake system according to one exemplary embodimentof the present disclosure. FIG. 3 is an exploded cross-sectional viewillustrating a piston unit according to one exemplary embodiment of thepresent disclosure is dissembled. A detailed structure of the pistonpump 1 for a brake system according to one exemplary embodiment of thepresent disclosure will be described in detail with reference to FIGS. 2and 3.

Referring to FIGS. 2 and 3, the piston pump 1 according to one exemplaryembodiment of the present disclosure includes all or some of a motor cam10, a piston housing 12, a piston unit 100, a sleeve unit 200, a checkvalve unit 300, and a filter 400.

The motor cam 10 is assembled to an output shaft of the motor (notshown) and rotates to perform cam movement when the motor operates. Dueto the cam movement of the motor cam 10, the piston unit 100reciprocates in the piston housing 12 in a longitudinal axis direction.The piston housing 12 is fixed to a vehicle body, and a space in whichthe elements of the piston pump 1 are assembled is included in thepiston housing 12.

The piston unit 100 includes all or some of a first piston 110, a secondpiston 120, a spring cap 130, an inlet spring 140, an inlet ball 150,and a first sealing 160.

One end of the first piston 110 is in contact with the motor cam 10, andthe first piston 110 reciprocates in the piston housing 12 in thelongitudinal axis direction by driving of the motor cam 10. The firstpiston 110 includes all or some of a sliding unit 112, a first couplingunit 114, and an inserting hole 116.

At least a part of the sliding unit 112 is surrounded by a secondsealing 520, a backup ring 540, and a guide ring 560. In this case,friction occurs due to the second sealing 520, backup ring 540, andguide ring 560. Furthermore, in the piston unit 100 according to thepresent disclosure, since a polishing process may be performed on onlythe first piston 110 where friction actually occurs, there is an effectof lowering a defect rate when the piston pump 1 is manufactured.

The first coupling unit 114 is arranged at the other end of the firstpiston 110 and is coupled to the second piston 120. A line through whichbrake oil is flowable is included in the first coupling unit 114.

The inserting hole 116 is defined between the sliding unit 112 and thefirst coupling unit 114. At least some of the brake oil introducedthrough an inlet line 14 passes through the inserting hole 116 and flowsto an inner line of the first coupling unit 114.

The second piston 120 is coupled to the first coupling unit 114 andoperates in conjunction with movement of the first piston 110. Thesecond piston 120 is configured to transmit hydraulic pressure, which isgenerated due to linear reciprocating movement of the first piston 110,to brake oil stored in an accommodation space 220. When the secondpiston 120 moves in a direction in which the brake oil is pressurized(leftward direction in FIG. 2), the brake oil stored in theaccommodation space 220 moves to an outlet line 16.

The second piston 120 includes all or some of a piston head unit 122, astep unit 124, and a second coupling unit 126.

The piston head unit 122 has a substantially hollow column shape, and atleast a part of the inlet ball 150 may be inserted into the piston headunit 122. An outer diameter of at least a part of the piston head unit122 is a first diameter D1.

The step unit 124 is disposed on an end portion of the piston head unit122 and may serve as a stopper for the spring cap 130. An outer diameterof at least a part of the step unit 124 is a second diameter D2 which isgreater than the first diameter D1.

The second coupling unit 126 is disposed inside the step unit 124 andcoupled to the first coupling unit 114. The first coupling unit 114 andthe second coupling unit 126 may be press-fitted. For example, the firstcoupling unit 114 may be coupled to the second coupling unit 126 in apress-fitting manner. However, the present disclosure is not necessarilylimited thereto, the first coupling unit 114 and the second couplingunit 126 may be screw-coupled using threads formed on the first couplingunit 114 and the second coupling unit 126.

In the present disclosure, although the first coupling unit 114 isillustrated as a male portion, and the second coupling unit 126 isillustrated as a female portion, the present disclosure is notnecessarily limited thereto. For example, the first coupling unit 114may be a female portion, and the second coupling unit 126 may be a maleportion.

Since the second piston 120 has the first diameter D1 and the seconddiameter D2, the structure is simple, and thus a manufacturing processcan be simplified.

The spring cap 130 is coupled to the piston head unit 122 and configuredto accommodate the inlet spring 140 and the inlet ball 150. Even whenthe second piston 120 reciprocates, the inlet spring 140 and the inletball 150 may not deviate from initial positions in the spring cap 130.

The spring cap 130 includes all or some of a piston coupling unit 132, acap head unit 134, a slope unit 136, and a flange unit 138.

The piston coupling unit 132 surrounds at least a part of the pistonhead unit 122 and is coupled to the piston head unit 122. An innerdiameter of the piston coupling unit 132 may be slightly smaller than orequal to the first diameter D1. Accordingly, the piston coupling unit132 and the piston head unit 122 may be press-fitted and coupled.However, the spring cap 130 and the second piston 120 do not need to bepress-fitted and may be screw-coupled.

The inlet spring 140 is accommodated in a space provided in the cap headunit 134. The inside and the outside of the cap head unit 134 fluidlycommunicate with each other. As an example, the cap head unit may beconfigured in the form of a cage. An inner diameter of at least a partof the cap head unit 134 has a third diameter D3 smaller than the firstdiameter D1.

The slope unit 136 is disposed between the piston coupling unit 132 andthe cap head unit 134, an inner diameter of the slope unit 136 decreasesin a direction from the piston coupling unit 132 toward the cap headunit 134. When the second piston 120 moves in the direction in which thesecond piston 120 presses the brake oil, the second piston 120 comesinto contact with an inner circumferential surface of the slope unit 136and no longer presses the inlet spring 140 and the inlet ball 150. Thatis, the slope unit 136 may serve as the stopper for the second piston120.

The flange unit 138 extends from an end portion of the piston couplingunit 132. The first sealing 160 may be disposed between the flange unit138 and the step unit 124. The first sealing 160 may prevent brake oil,which is introduced through the inlet line 14, from being introducedinto the accommodation space 220.

One side of the inlet spring 140 is in contact with the inlet ball 150,and the other side thereof is fixed to a ceiling of the spring cap 130.The inlet spring 140 presses the inlet ball 150 in a direction in whichthe motor cam 10 is installed to elastically support the inlet ball 150.

Due to the inlet spring 140, the inlet ball 150 presses the secondpiston 120 in the direction in which the motor cam 10 is installed. Theinlet ball 150 restricts a flow of brake oil discharged from the pistonhead unit 122 to serve as a check valve.

The sleeve unit 200 is disposed to surround at least a part of thepiston unit 100. The sleeve unit 200 includes all or some of theaccommodation space 220, a return spring 240, and a discharging hole260.

The accommodation space 220 is included in the sleeve unit 200 to storebrake oil. When the piston unit 100 is moved by the motor cam 10 in adirection in which the brake oil stored in the accommodation space 220is pressurized, the accommodation space 220 may function as ahigh-pressure chamber.

The return spring 240 is disposed in the accommodation space 220, oneend of the return spring 240 is in contact with the spring cap 130, andthe other end thereof is fixed to the ceiling in the sleeve unit 200.The return spring 240 elastically supports the spring cap 130 in thedirection in which the motor cam 10 is installed. After the piston unit100 is moved toward the check valve unit 300 by the motor cam 10, andwhen the piston unit 100 is returned to an initial position, the returnspring 240 provides an elastic force to press the piston unit 100 in thedirection in which the motor cam 10 is installed.

The discharging hole 260 is defined in one surface of the sleeve unit200, and the brake oil, which passes through the discharging hole 260and is stored in the accommodation space 220, may be discharged to theoutside of the sleeve unit 200.

The check valve unit 300 is disposed to face one surface of the sleeveunit 200. The check valve unit 300 is configured so that, when apressure of the brake oil stored in the accommodation space 220increases, the brake oil is discharged to the outside of the sleeve unit200. In this case, the check valve unit 300 may be configured in one ofvarious shapes within the technical idea that the pressure of the brakeoil is increased to be discharged to the outside of the sleeve unit 200.The check valve unit 300 according to the present disclosure includes anoutlet spring 320 and an outlet ball 340.

The outlet spring 320 and the outlet ball 340 are disposed between thecheck valve unit 300 and the sleeve unit 200. The outlet spring 320elastically supports the outlet ball 340 in the direction in which themotor cam 10 is installed. The outlet ball 340 has a spherical shape andis disposed to face the discharging hole 260. The outlet ball 340controls opening and closing of the outlet line 16.

The filter 400 is disposed to surround at least a part of the pistonunit 100. When brake oil flows in a direction from inlet line 14 towardthe inserting hole 116, the brake oil passes through the filter 400. Asthe brake oil passes through the filter 400, foreign matter included inthe brake oil may be filtered.

In addition, the piston pump 1 according to the present disclosure mayfurther include the second sealing 520, the backup ring 540, and theguide ring 560.

The second sealing 520 is disposed between the piston housing 12 and thesliding unit 112 and may block a flow of brake oil which flows along anouter side of the piston unit 100.

The backup ring 540 is disposed adjacent to the second sealing 520 andsupports the second sealing 520 when the second sealing 520 receivespressure.

The guide ring 560 is disposed adjacent to the backup ring 540 andguides movement of the piston unit 100 so that the piston unit 100 moveslinearly when reciprocating.

Hereinafter, an operation state of the piston pump 1 according to oneembodiment of the present disclosure will be described in detail.

FIG. 4 is a cross-sectional view illustrating a state in which brake oilis supplied to the accommodation space of the sleeve unit according toone exemplary embodiment of the present disclosure.

A small arrow illustrated in FIG. 4 denotes a flow direction of brakeoil, and a large arrow denotes a movement direction of the piston unit100. Referring to FIG. 4, as the motor rotates, the eccentric motor cam10 is rotated in one direction (indicated by a curved arrow of FIG. 4).By the rotation of the motor cam 10, the first piston 110 and the secondpiston 120 are moved in the direction (rightward direction in FIG. 4) inwhich the motor cam 10 is installed. In this case, the pressure of thebrake oil present in the accommodation space 220 of the sleeve unit 200decreases. Accordingly, the brake oil sequentially passes through theinlet line 14, the inserting hole 116, and the piston head unit 122. Asthe first piston 110 and the second piston 120 are moved in thedirection in which the motor cam 10 is installed, the inlet ball 150 isseparated from the second piston 120. The brake oil moved to an innerspace of the piston head unit 122 passes through a space between theinlet ball 150 and the second piston 120, which are separated, andsequentially flows through the spring cap 130 and the accommodationspace 220.

FIG. 5 is a cross-sectional view illustrating a state in which the brakeoil stored in the accommodation space of the sleeve unit according toone exemplary embodiment of the present disclosure is discharged to theoutside of the sleeve unit.

A small arrow illustrated in FIG. 5 denotes the flow direction of thebrake oil, and a large arrow denotes the movement direction of thepiston unit 100. Referring to FIG. 5, by the rotation of the motor cam10, the piston unit 100 is moved in a direction toward the check valveunit 300. By forward movement of the piston unit 100, the brake oilstored in the accommodation space 220 of the sleeve unit 200 iscompressed. Accordingly, the pressure applied to the outlet ball 340increases, and the outlet spring 320 is compressed. Since the outletball 340 is moved in a direction away from the discharging hole 260, thesleeve unit 200 and outlet ball 340 are separated and a space is formed.The brake oil is discharged between the formed space and moves to theoutlet line 16. The brake oil passing through the outlet line 16 movesbetween the piston housing 12 and the sleeve unit 200.

FIG. 6 is a schematic cross-sectional view illustrating a structure of apiston pump for a brake system according to another exemplary embodimentof the present disclosure.

Referring to FIG. 6, a piston unit 600 of a piston pump 6 according toanother embodiment includes a first piston 610, a second piston 620, anda spring cap 630.

The first piston 610 according to another embodiment of the presentdisclosure includes a sliding unit 612 and a first coupling unit 614.

One end of the sliding unit 612 is in contact with the motor cam 10, andthe sliding unit 612 reciprocates in a longitudinal axis direction dueto rotational movement of a motor cam 10.

The first coupling unit 614 is disposed to extend from the other end ofthe sliding unit 612 in a direction in which the first coupling unit 614presses an inner portion of a sleeve unit 200. At least a part of thefirst coupling unit 614 is configured to be press-fitted into one end ofthe second piston 620. A coupling relationship between the first piston610 and the second piston 620 will be described in detail below.

Since shapes and technical features of the second piston 620 and thespring cap 630 according to another embodiment of the present disclosureare the same as or similar to those of the second piston 120 and thespring cap 130 according to one embodiment, detailed descriptionsthereof will be replaced with the descriptions of one embodiment.

FIG. 7A is an exploded perspective view illustrating a part of thepiston unit according to another exemplary embodiment of the presentdisclosure. FIG. 7B is a perspective view illustrating some coupledparts of the piston unit according to another embodiment of the presentdisclosure. FIG. 8A is a longitudinal sectional view of the part of thepiston unit of FIG. 7B taken along line VIIIa-VIIIa′. FIG. 8B is alongitudinal sectional view of the part of the piston unit of FIG. 7Btaken along line VIIIb-VIIIb′.

Referring to FIGS. 7 and 8, a punch process may be performed on one endof the first piston 610 so that brake oil flows. In this case, at leasta part of the punched one end is coupled to the second piston 620 asillustrated in FIG. 7B. Further, the second piston 620 according toanother embodiment of the present disclosure is punched in a directionperpendicular to the longitudinal axis direction, and a separate lineformed to be parallel to the longitudinal axis direction is also notneeded. Accordingly, there are effects of simplifying a manufacturingprocedure and lowering a defect rate when the piston pump ismanufactured.

Still further, as illustrated in FIG. 8B, at least a part of the firstpiston 610 according to another embodiment of the present disclosure ispress-fitted into the second piston 620. Here, coupling of the firstpiston 610 and the second piston 620 illustrated in FIG. 6 may beunderstood with reference to a cross-section illustrated in FIG. 8A.

Although exemplary embodiments of the present disclosure have beendescribed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions, and substitutions arepossible, without departing from the idea and scope of the claimedinvention. Therefore, exemplary embodiments of the present disclosurehave been described for the sake of brevity and clarity. The scope ofthe technical idea of the present embodiments is not limited by theillustrations. Accordingly, one of ordinary skill would understand thescope of the claimed invention is not to be limited by the aboveexplicitly described embodiments but by the claims and equivalentsthereof.

What is claimed is:
 1. A piston pump comprising: a piston unitconfigured to reciprocate in a piston housing by driving of a motor cam;a sleeve unit disposed to surround at least a part of the piston unitand having an accommodation space in which brake oil is stored; and acheck valve unit disposed to face the sleeve unit and configured todischarge the brake oil to an outside of the sleeve unit when a pressureof the brake oil stored in the accommodation space of the sleeve unitincreases, wherein the piston unit includes a first piston having afirst end in contact with the motor cam and configured to reciprocate, asecond piston having a first end coupled to a second end of the firstpiston and operating in conjunction with reciprocating movement of thefirst piston to press the brake oil stored in the accommodation space ofthe sleeve unit, and a spring cap coupled to a second end of the secondpiston and disposed to accommodate an inlet spring therein.
 2. Thepiston pump of claim 1, wherein the second piston includes: a pistonhead unit having at least a part of which an outer diameter is a firstdiameter; and a step unit having at least a part of which an outerdiameter is a second diameter greater than the first diameter.
 3. Thepiston pump of claim 2, wherein the spring cap includes: a pistoncoupling unit coupled to at least a part of the piston head unit; a caphead unit disposed to accommodate the inlet spring, wherein an insideand an outside of the cap head unit are configured to fluidlycommunicate with each other; and a slope unit extending between thepiston coupling unit and the cap head unit and having an inner diameterwhich decreases in a direction from the piston coupling unit toward thecap head unit.
 4. The piston pump of claim 3, wherein the inner diameterof at least a part of the cap head unit is a third diameter smaller thanthe first diameter.
 5. The piston pump of claim 3, wherein the springcap includes a flange unit extending from an end portion of the pistoncoupling unit.
 6. The piston pump of claim 5, wherein the piston unitincludes a first sealing disposed between the flange unit and the stepunit.
 7. The piston pump of claim 3, wherein the piston head unit andthe piston coupling unit are press-fitted to be coupled.
 8. The pistonpump of claim 1, wherein the piston unit includes an inlet ball disposedbetween the second piston and the spring cap and pressed by the inletspring in a direction toward the second piston.
 9. The piston pump ofclaim 1, wherein: the first piston includes a first coupling unitcoupled to at least a part of the second piston; the second pistonincludes a second coupling unit disposed to surround the first couplingunit; and the first coupling unit and the second coupling unit arepress-fitted to each other.
 10. The piston pump of claim 1, furthercomprising: a second sealing disposed between the piston housing and thefirst piston; a backup ring disposed between the piston housing and thefirst piston and configured to support the first piston; and a guidering disposed between the piston housing and the first piston andconfigured to guide reciprocating movement of the first piston.
 11. Apiston pump comprising: a piston unit configured to reciprocate in apiston housing by driving of a motor cam; a sleeve unit disposed tosurround at least a part of the piston unit, and having an accommodationspace in which brake oil is stored; and a check valve unit disposed toface the sleeve unit and configured to discharge the brake oil to anoutside of the sleeve unit when a pressure of the brake oil stored theaccommodation space of the sleeve unit increases, wherein the pistonunit includes a first piston having a first end in contact with themotor cam and configured to reciprocate, a second piston having a firstend press-fitted and coupled to a second end of the first piston andoperating in conjunction with reciprocating movement of the first pistonto press the brake oil stored in the accommodation space of the sleeveunit, and a spring cap disposed to accommodate an inlet spring thereinand coupled to a second end of the second piston.
 12. The piston pump ofclaim 11, wherein the first end of the first piston is punch-processedin a direction perpendicular to a longitudinal axis direction so thatthe brake oil is flowable.